Quality gaps that are relevant to the ambulatory setting include a high incidence of adverse drug events and lack of compliance with established guidelines for preventive care, chronic disease management, and test result follow-up. Clinical decision support systems (CDSS) and ambulatory computerized physician order entry (ACPOE) have been touted as powerful interventions to address these concerns. However, doubts exist about the efficacy of these systems in the ambulatory setting, especially when they exist in isolation. Also, despite the evidence of the impact of inpatient CPOE, the impact of ACPOE has not been well studied. Moreover, the adoption of CDSS and ACPOE systems is slow, and their value proposition remains uncertain. Tightly integrating CDSS with ACPOE serves as a promising strategy to improve quality and efficiency in the ambulatory setting by facilitating physician action. When ACPOE is linked with CDSS, clinicians can be prompted at various points during their workflow about the desirable course of action and simultaneously can be given the opportunity to execute the action (by ordering it) with minimal effort. The applicant hypothesizes that the value of ACPOE integrated with advanced CDSS lies not only in improved medication safety and guideline compliance, but also improved efficiencies for the individual provider and the health-care system. The applicant further hypothesizes that the value added by these systems overall outweighs their costs. The applicant propose to study the impact of integrating ACPOE with advanced CDSS on important safety and quality domains in the ambulatory setting using randomized controlled trials. In addition, the applicant will evaluate the impact on organizational efficiency, physician workflow and satisfaction, and perform a cost-benefit analysis. Partners Healthcare has in place a highly developed outpatient electronic medical record called the Longitudinal Medical Record (LMR) that has been used by primary care physicians since 2000 to track their patients' problems, medications, allergies, and health maintenance data. The LMR also embeds within itself CDSS, such as alerts, reminders, and results tracking, and is currently piloting ACPOE. This innovative technology environment combined with a long record of excellence in patient safety research makes Partners uniquely suited to study the impact of integrating CDSS with ACPOE. Given the diversity of practices, these findings will be generalizable to other organizations and will speed the adoption of these systems.